 In this lecture we will study about the ecosystem, its definition, its structure and its different components. An ecosystem can be defined as a community of living organism, living in one environment and working in conjunction of the non-living components of that area. The non-living components of a particular area or a habitat involves temperature, water, heat, light, photo-period, soil, topography, etc. Both these living components which include the animal, plants and microbes they interact with the non-living components of that particular ecosystem and they are completely integrated with each other and they depend upon each other for their needs. Living components actually they depend upon the non-living components for their survival. While studying an ecosystem we need to know about the two important definitions. First one is the population. A population can be defined as a group of individuals belonging to same species occupying the same space in a particular time period. While a community which is the second important term in ecosystem it is defined as a group of populations belonging to different species occupying the same space in a particular time period. So in this image a complete picture of one ecosystem has been given involving its living and non-living components. So initially that the first stage there is an individual belonging to a certain species and an individual in on its own is interacting with the non-living components of an ecosystem. A group of individuals from same species they make population while different populations they make the community. All these different communities they are interacting with all the physical factors in that particular area or a habitat and thus they make an integrated system which is known as ecosystem. Any ecosystem is controlled by two categories of factors. One is external and second is internal. In the internal category it involves the factors involving climate and topography of that particular environment. Topography means the landscape features of soil and they play an important role in distribution of animal or structure of an ecosystem. While the internal category it involves the biodiversity which means types of species. The population size of these species there might be a disease outbreak, different gene pools and the reproductive rate of any species which affect any ecosystem. External factors are independent of internal factors so they don't influence internal factors but internal factors which have been mentioned above they are dependent upon the physical factors of any environment or an ecosystem for their existence. Because of living in a particular set of physical factors all the animals and plants which are the living component in that ecosystem they have to adapt themselves according to the physical factors of that environment. Therefore we get distinct biological communities and these distinct biological communities are known as biomes. Each biome is formed in response to the specific external factors present in that environment. In this video we will have the concept of different biomes and the physical factors which are affecting these biomes and the living components. In this video we have seen that there are two types of ecosystem one is aquatic and other one is terrestrial. Aquatic ecosystems can be divided into further two types marine ecosystem and freshwater ecosystem. Terrestrial ecosystems are of various types and we have seen they are very much controlled by the temperature, rainfall and the availability of fresh water. So these internal factors they are actually controlled by a feedback loop other than the external factors or the physical factors of an ecosystem. This feedback loop actually can be explained that if population size of one species is increasing by utilizing the resources so it put pressure on the food and shelter all these available resources for that particular species. Reduction in availability of these resources will ultimately reduce the population size of that particular species through that feedback loop or we could say it is a negative feedback mechanism. Any ecosystem is a dynamic entity and there are continuously changes happening in any ecosystem whether it is aquatic or terrestrial environment. So the both type of ecosystems are subjected to disturbances. Mostly these disturbances they occur because of changes in physical factors or it might be a natural catastrophe. However after every disturbance ecosystem has a capacity to recover itself by increasing the number of population sizes and the migration or immigration of animals and plants. And this process of recovery is known as succession. Therefore ecosystem is reviving itself automatically.